The invention relates to the manufacture of optical data storage disks.
Optical data storage disks have gained widespread acceptance for the storage, distribution and retrieval of large volumes of information. Optical data storage disks include, for example, audio CD (compact disc), CD-R (CD-recordable), CD-ROM (CD-read only memory), DVD (digital versatile disk or digital video disk) media, DVD-RAM (DVD-random access memory), and various types of rewritable media, such as magneto-optical (MO) disks and phase change optical disks. Some newer formats for optical data storage disks are progressing toward smaller disk sizes and increased data storage density.
Optical data storage disks can be produced by first making a master disk that has a surface pattern that represents encoded data on the master disk surface. The surface pattern, for instance, may be a collection of grooves that define master pits and master lands. The master disk is typically created by a relatively expensive mastering process.
After creating a suitable master, that master can then be used to make a stamper. The stamper has a surface pattern that is the inverse of the surface pattern encoded on the master. The stamper, then, can be used to stamp large quantities of replica disks in a mass production stamping process such as an injection molding process or a rolling bead process. Each replica disk may contain the data and tracking information that was encoded on the master.
During a stamping process, an inverse of the surface pattern on the stamper becomes molded into each replica disk, forming a collection of grooves that define lower reflectance xe2x80x9cpitsxe2x80x9d within a plane of higher reflectance xe2x80x9clands.xe2x80x9d Typically, the stamped side of the disk is then coated with a reflectance layer, such as a thin layer of aluminum, and in the case of a CD, followed by a protective layer of lacquer. Data tracks on an optical disk can be arranged in a spiral manner originating at the disk center and ending at the disk outer edge, or alternatively, a spiral track can originate at the disk outer edge and end at the disk center. The data also can lie in a series of concentric tracks spaced radially from the disk center.
In general, the invention is directed toward techniques for stamping optical data storage disks. A master is first created to include several distinct information regions etched upon a master surface. The master is then used to create one or more stampers. The stampers include a number of distinct stamper regions in locations corresponding to locations of the distinct information regions on the master. The distinct information regions may be substantially circular in shape. The stamper may then be used to create additional stampers, or ultimately, to create a number of first replica disks.
A first replica disk includes distinct replicated regions in locations substantially corresponding to locations of the distinct information regions on the master. These distinct replicated regions can then be separated from the first replica disk to create a number of second replica disks that are smaller than the first disk. For example, the replicated regions may be separated from the first disk by die punching, laser cutting or mechanical cutting, i.e., using a lathe or carbide cutting tool. Other ways of separating the replicated regions could also be used. The final result is a number of second replica disks having sizes that substantially correspond to the sizes of the distinct information regions that were originally etched upon the master surface. Thus, a single replica disk can be stamped and then subdivided into multiple replica disks.
In one embodiment, a method includes creating a master having distinct information regions etched upon a surface, and creating a stamper from the master. The distinct information regions may be etched upon the surface of the master in an evenly spaced arrangement, wherein the distance between the center of the master and the centers of the distinct information regions are substantially equal. The method may also include stamping a first disk with the stamper, the first disk including replicated regions in locations substantially corresponding to locations of the distinct information regions on the master. In addition, the method may include separating the replicated regions from the first disk to create a number of second disks from the first disk.
Creating the master may include coating a master glass with photoresist and placing the master glass in a master glass carrier such that the center of the master glass is offset from the center of the master glass carrier. A first distinct information region can then be exposed to a laser on the master glass. The master glass is then rotated relative to the master glass carrier, and a second distinct information region can then be exposed. After exposing a number of information regions, the master glass can be developed to define the information regions on the master glass.
In other embodiments, the invention comprises masters, stampers, or optical disks. For example, a master may include multiple distinct information regions etched upon a surface in an evenly spaced arrangement, wherein distances between a center of the master and centers of the information regions are substantially equal. A stamper may include a number of distinct stamper regions in an evenly spaced arrangement, wherein the distance between the center of the stamper and the centers of the distinct stamper regions are substantially equal. Similarly, an optical disk may include a number of distinct replicated regions in an evenly spaced arrangement, wherein a distance between a center of the optical disk and centers of the replicated regions are substantially equal.
The invention provides several advantages. For example, the invention can generally promote more efficient optical disk manufacturing. In particular, a single stamping process can yield a number of replica disks. Smaller disks are simply die punched or otherwise removed from a stamped disk that includes a number of distinct replicated regions. In addition, the invention can utilize many existing machines and processes to fabricate newer optical disks that are sized much smaller than the disks that existing machines were originally designed to create. For example, conventional CD or DVD stamping tools can be utilized to stamp the first disks. A number of smaller disks can then be removed from each first disk. Utilizing existing stamping tools can significantly reduce overhead associated with the development of smaller optical disks for use with new formats.
In addition, the invention may realize optical disks that have improved characteristics. In particular, center holes in the smaller optical disks can be punched after a reflective layer is deposited on the smaller disks. This can avoid the accumulation of metal in the center holes of the disk, which may occur if a conventional process is used to create the smaller disks. The accumulation of metal in the center hole of a disk is undesirable if a hub is to be attached to the center hole, e.g., which is often the case for formats in which the smaller disks are ultimately housed in a data cartridge.
Removing a number of smaller disks from a first disk that includes a number of replicated regions can also improve disk quality of the smaller disks. For example, the smaller disks may not exhibit disk imperfections or thickness variations typically associated with edges of molded disks. In addition, overexposure of photoresist on the master can be avoided in the case where the innermost regions of the smaller disks are exposed to a laser. In particular, laser reflection off of a center hub, which can overexpose the photoresist, can be avoided if the replicated regions are located at a distance from the center of the master.